You may see a higher than expected pulse frequency from your Advanced Pulse WattNode. There are several possible reasons for this.

Power Over-Range

Your load is consuming (or generating) more than the nominal full-scale power. For example, if you have a WNB-3Y-208-P with 30A CTs, the nominal line voltage is 120 VAC and the nominal full-scale current is 30 amps. Suppose your actual line voltage is 124 VAC and your current is 35 amps and the power factor is 1.00. Then you are consuming 124 * 35 = 4340 watts, while the nominal full-scale power for the WattNode is 120 * 30 = 3600. If your WattNode has a full-scale pulse frequency of 4.0 Hz, it would generate 4.82 Hz with this over-range condition.

Under extreme over-range conditions, the pulse WattNode can generate up to double the nominal pulse frequency.

Counting Rising and Falling Edges

We define a pulse as one full ON/OFF cycle of the output. Some data loggers can be configured to count both the rising and falling edges and so report a frequency twice as high.

If this is happening, you can either try to configure your data logger to only count rising edges or you can adjust your scale factors downward by a factor of 2.0 to correct the results.

Non-Standard WattNode Pulse Frequency

Pulse WattNodes are available with full-scale pulse output frequencies from a fraction of a hertz up to 600 Hz. The standard frequency is 4.0 Hz, but you should check the label (below the model number) to see if your WattNode has been ordered with a custom pulse frequency (for example: Opt Hz=20). If you don’t see any options, then the pulse frequency will be the standard 4.0 Hz.

Noise on the Pulse Lines

Noise on the pulse output wires is rare, but it can happen in a few cases:

  • You have long (more than 10 meters) unshielded wires on the pulse output.
  • There is high electromagnetic noise in the area (variable speed drives can cause problems).
  • If your data logger or monitoring device has a very low sense current. This is most common with battery powered devices.

If you suspect this, you might try moving the data logger to within a meter or so of the WattNode and using a short connecting wire to see if the problem goes away. You could also try unhooking the wires from the WattNode to see if there is enough electrical noise to cause false pulse detection with nothing connected.

See Also